It is our ultimate goal to define the mechanisms by which EBV establishes long-term latency in the host and how this process goes awry leading to disease. In this proposal, we aim to define the molecular basis for the unique interactions between EBV latent nuclear proteins and the cellular DNA binding protein RBPJ. It is our central hypothesis that the viral EBNA2 and EBNA3 proteins compete for a unique molecular surface relative to that used by Notch to bind to RBPJ. We propose that this binding surface is required for EBV to establish latency in the B- cell reservoir. We have formulated our central hypothesis based on structural studies of the interface between Notch and RBPJ coupled with biochemical studies of the EBNA proteins with RBPJ. We have synthesized these existing data to establish a structural model that we plan to test in this application. The rationale for this proposed research is that defining the high- resolution molecular interfaces unique to the EBV nuclear proteins relative to Notch will allow us to build a higher order model for how EBV regulates viral and cellular transcription to establish and maintain latency. My laboratory is well positioned to pursue these molecular studies as I have both a strong background in structural biology as well as a track record in the study of EBV latency. We plan to test our hypothesis and complete the objectives outlined in this proposal through the following two specific aims: 1) Solve the high-resolution crystal structures of EBNA2 and the EBNA3 homology domain bound to RBPJ and 2) Define the unique EBNA2, EBNA3, and Notch binding surfaces on RBPJ.